The objectives of this study are to document the natural history and determine if the photocoagulation treatment is useful in the management of branch vein occlusion and its complications. The treatment by argon laser photocoagulation will be evaluated for the management of: a) Major branch vein occlusion without neovascularization; 1) Improve or maintain visual acuity; 2) Improve or prevent macular edema; 3) Prevent the development of neovascularization. b) Major branch vein occlusion with neovascularization; 1) Improve or maintain visual acuity; 2) Control or destroy neovascularization; 3) Prevent vitreous hemorrhage and/or retinal detachment; 4) Improve or prevent macular edema. c) Macular branch vein occlusion with macular edema and decreased vision; 1) Improve or maintain visual acuity; 2) Improve macular edema.